Arrangement and method for producing a three-dimensional product

ABSTRACT

An arrangement and method for production of three-dimensional bodies by successive fusing together of selected areas of a powder bed, which parts correspond to successive cross sections of the three-dimensional body, which method comprises the following method steps: application of powder layers to a work table, supplying energy from a radiation gun according to an operating scheme determined for the powder layer to said selected area within the powder layer, fusing together that area of the powder layer selected according to said operating scheme for forming a cross section of said three-dimensional body, a three-dimensional body being formed by successive fusing together of successively formed cross sections from successively applied powder layers.

TECHNICAL FIELD

The invention relates to an arrangement and a method for production of athree-dimensional product by successive fusing together of selectedparts of powder layers applied to a work table.

BACKGROUND ART

An arrangement for producing a three-dimensional product by successivefusing together of selected parts of powder layers applied to a worktable is previously known from, for example, U.S. Pat. No. 4,863,538.The arrangement comprises a work table on which said three-dimensionalproduct is to be built up, a powder dispenser which is arranged so as todistribute a thin layer of powder on the work table for forming a powderbed, a radiation gun for delivering energy to the powder, fusingtogether of the powder then taking place, means for guiding the beamemitted by the radiation gun over said powder bed for forming a crosssection of said three-dimensional product by fusing together parts ofsaid powder bed, and a control computer in which information aboutsuccessive cross sections of the three-dimensional product is stored.The three-dimensional product is built up by fusing together selectedparts of successive powder layers applied. The control computer isintended to control deflection means for the beam generated by theradiation gun over the powder bed according to an operating scheme whichreproduces a predetermined pattern. When the operating scheme has fusedtogether a desired area of a powder layer, a cross section of saidthree-dimensional product has been formed. A three-dimensional productis formed by successive fusing together of successively formed crosssections from powder layers applied successively by the powderdispenser.

An arrangement for producing a three-dimensional product wheremeasurement of the surface structure and the surface temperature of thethree-dimensional body produced is permitted during the manufacturingprocedure is known from SE 0001557-8. By using the arrangement describedtherein, increased correspondence of the shape of the three-dimensionalbodies produced in relation to the intended shape is made possible. Inthe process for manufacturing the three-dimensional products, however,it has been found that surface stresses in the manufactured product giverise to shape deviations and also internal stresses in the product whichcan give rise to the initiation of crack formation.

BRIEF DESCRIPTION OF THE INVENTION

One object of the invention is to provide a method for production ofthree-dimensional bodies where reduction of the occurrence of surfacestresses and shape deviations induced by these and also the occurrenceof internal stresses in the end product is made possible. This object isachieved by an arrangement according to the characterizing part ofpatent claim 1. By virtue of, in a method for production ofthree-dimensional bodies, dividing the selected area of a powder bedcorresponding to a cross section of the three-dimensional body into aplurality of smaller part areas which consist of an inner area and anedge, it is made possible to provide operating schemes where the energysupply can take place in an advantageous way in order to ensure that theworking temperature at the top layer of the body to be manufactured canbe kept within an acceptable temperature range. The possibility ofkeeping the working surface within a narrow temperature range means thatsurface stresses in the manufactured product can be reduced. Surfacestresses give rise to shape deviations and also internal stresses in theproduct which can give rise to the initiation of crack formation.

An inner area is preferably treated in a process step which is separatefrom the treatment of the edge which surrounds the inner area. Separateprocess step means that the edge is finished either before or after theinner area.

According to a first preferred embodiment of the invention, by virtue offusing together the inner area of a set of adjacent part areas in afirst process step, and then fusing together the edges which connectsaid part areas in a second, subsequent process step, athree-dimensional body is obtained after manufacture which has a lowerdegree of internal stresses than if the selected area were fusedtogether using a linear sweep pattern along the entire surface of theselected area. This is due to the fact that two adjacent areas, whichhave been formed into a solid body, are freely movable until these twoadjacent areas are joined together by fusing together the material whichforms the common boundary line. The joining together thus takes place ina stress-free state.

According to a second embodiment, the priority for treating the smallerpart areas which constitute a selected cross section is determined withthe aid of a random number generator. This process ensures that theheating of the entire surface to be treated takes place in a relativelyhomogeneous way in contrast to if systematic planning of fusing togetherof adjacent areas in close succession consecutively one after anothertakes place. This method is especially advantageous if the selected areais divided into a very great number of smaller part areas, preferablymore than 100 or 1000. The random process can also include intelligentselection where areas which are adjacent to an area which has just beenheated are given less probability of being picked as the next area. Aheat camera used in the method can be arranged so as to measure thetemperature of all the areas included and then adjust probabilitiesdepending on the temperature of each smaller area. If N areas are usedand the bed temperature varies from T₀, which corresponds to theuninfluenced bed temperature, to T_(S), which corresponds to thetemperature of an area which has just been fused, the probability of anarea being selected is preferably adjusted to P(i)=T_(S)−Ti/Σ(T_(s)−Tn).An area which has just been fused will then be given the probability 0of being heated again. The probability for all cold areas is equal, andthe probability of an area being selected to be the next area fortreatment is linearly dependent on the temperature in relation to thefusion temperature.

According to a third embodiment, which can advantageously be used if alower degree of homogeneity is required for parts of the interior of thebody, the edges can instead be fused together in a first process stepfor a number of consecutive powder layers, after which the inner areasof said consecutive powder layers are fused together in a common secondprocess step for said consecutive powder layers. By means of thisprocedure, a body is obtained with a smooth outer surface and internalpartitions corresponding to the inner edges where the internalpartitions have a high degree of solidity. The intermediate inner areashave a lower degree of fusing together, it being possible for a certainporosity to be obtained. As the product in this case is advantageouslynot entirely homogeneous, the risk of the appearance of internalstresses is reduced as a certain capacity for movement in the innerporous structure allows internal stresses to be attenuated.

According to a fourth embodiment of the invention, the inner area isfused together in the course of a movement pattern for the focal pointof the beam of the radiation gun which comprises a main movementdirection and an interference term which is added to said main movementdirection and has a component in a direction at right angles to the mainmovement direction. The interference term has a time mean valuecorresponding to zero drift from the main movement direction. The mainmovement direction has a propagation speed which preferably correspondsto the propagation speed of a fusion zone of a treated material. Themain movement direction can have any curve shape, for examplerectilinear, curved, circular. The appearance of the main movementdirection is adapted to the shape of the object to be created. However,the interference term is not adapted to the shape of the object but isdesigned in order to provide a more favorable local heat distribution inan area around the focal point. The movement pattern of the beam thusensures that the energy of the radiation gun is supplied to the powderlayer with more uniform intensity, the risk of overheating beingreduced. This in turn reduces the risk of the appearance of shapedeviations and stresses in the end product. According to a preferredembodiment, the edge is fused together in the course of a mainlyrectilinear movement, which follows the shape of the edge, of the beamof the radiation gun. By virtue of the edge being fused together in thecourse of a movement which follows the shape of the edge, it is ensuredthat the lateral surface of the finished body is smooth.

According to another preferred embodiment of the invention, an energybalance is calculated for each powder layer, it being determined in thecalculation whether energy fed into the powder layer when said supply ofenergy from a radiation gun according to an operating scheme determinedfor the powder layer for fusing together that area of the powder layerselected according to said operating scheme takes place is sufficient tomaintain a defined working temperature of the next layer, informationbeing obtained which makes it possible to maintain a definedtemperature. By maintaining a defined working temperature, that is tosay a surface temperature within a given defined temperature range,during the production of all the layers, it is ensured that theoccurrence of surface stresses which arise when cooling of thethree-dimensional body is too great is reduced. This in turn leads tothe end product having a reduced occurrence of shape deviations and alsoa reduced occurrence of internal stresses in the end product.

Another object of the invention-is to provide an arrangement forproduction of three-dimensional bodies where reduction of the occurrenceof surface stresses and shape deviations induced by these and also theoccurrence of internal stresses in the end product is made possible.This object is achieved by an arrangement according to thecharacterizing part of patent claim 11.

According to a first preferred embodiment of the invention, theradiation gun is arranged so as to fuse together the inner area of a setof adjacent part areas in a first process step, and then to fusetogether the edges which connect said part areas in a second, subsequentprocess step, a three-dimensional body being obtained after manufacturewhich has a lower degree of internal stresses than if the selected areawere fused together using a linear sweep pattern along the entiresurface of the selected area. This is due to the fact that two adjacentareas, which have been formed into a solid body, are freely movableuntil these two adjacent areas are joined together by fusing togetherthe material which forms the common boundary line. The joining togetherthus takes place in a stress-free state.

According to a second embodiment, a random number generator is arrangedso as to determine the priority for treating the smaller part areaswhich constitute a selected cross section. This process ensures that theheating of the entire surface to be treated takes place in a relativelyhomogeneous way in contrast to if systematic planning of fusing togetherof adjacent areas in close succession consecutively one after anothertakes place. This method is especially advantageous if the selected areais divided into a very great number of smaller part areas, preferablymore than 100 or 1000. The random process can also include intelligentselection where areas which are adjacent to an area which has just beenheated are given less probability of being picked as the next area. Aheat camera used in the method can be arranged so as to measure thetemperature of all the areas included and then adjust probabilitiesdepending on the temperature of each smaller area. If N areas are usedand the bed temperature varies from To, which corresponds to theuninfluenced bed temperature, to T_(S), which corresponds to thetemperature of an area which has just been fused, the probability of anarea being selected is preferably adjusted to P(i)=T_(S)−Ti/Σ(T_(S)−Tn).An area which has just been fused will then be given the probability 0of being heated again. The probability for all cold areas is equal, andthe probability of an area being selected to be the next area fortreatment is linearly dependent on the temperature in relation to thefusion temperature.

According to a third embodiment, which can advantageously be used if alower degree of homogeneity is required for parts of the interior of thebody, the radiation gun is arranged so as to fuse together the edges ina first process step for a number of consecutive powder layers, afterwhich the inner areas of said consecutive powder layers are fusedtogether in a common second process step for said consecutive powderlayers. By means of this procedure, a body is obtained with a smoothouter surface and internal partitions corresponding to the inner edgeswhere the internal partitions have a high degree of solidity. Theintermediate inner areas have a lower degree of fusing together, itbeing possible for a certain porosity to be obtained. As the product inthis case is advantageously not entirely homogeneous, the risk of theappearance of internal stresses is reduced as a certain capacity formovement in the inner porous structure allows internal stresses to beattenuated.

According to a fourth embodiment of the invention, the operating schemeis arranged so as to provide a movement pattern for the focal point ofthe beam of the radiation gun which comprises a main movement directionand an interference term which is added to said main movement directionand has a component in a direction at right angles to the main movementdirection. The interference term has a time mean value corresponding tozero drift from the main movement direction. The main movement directionhas a propagation speed which preferably corresponds to the propagationspeed of a fusion zone of a treated material. The main movementdirection can have any curve shape, for example rectilinear, curved,circular. The appearance of the main movement direction is adapted tothe shape of the object to be created. However, the interference term isnot adapted to the shape of the object but is designed in order toprovide a more favorable local heat distribution in an area around thefocal point. The movement pattern of the beam thus ensures that theenergy of the radiation gun is supplied to the powder layer with moreuniform intensity, the risk of overheating being reduced. This in turnreduces the risk of the appearance of shape deviations and stresses inthe end product. According to a preferred embodiment, the edge is fusedtogether in the course of a mainly rectilinear movement, which followsthe shape of the edge, of the beam of the radiation gun. By virtue ofthe edge being fused together in the course of a movement which followsthe shape of the edge, it is ensured that the lateral surface of thefinished body is smooth.

In a preferred embodiment of the invention, the control computerincluded in the arrangement is arranged so as to calculate an energybalance for each powder layer, it being determined in the calculationwhether energy fed into the powder layer when said supply of energy froma radiation gun according to an operating scheme determined for thepowder layer for fusing together that area of the powder layer selectedaccording to said operating scheme takes place is sufficient to maintaina defined working temperature of the next layer, information beingobtained which makes it possible to maintain a defined workingtemperature. By maintaining a defined working temperature, that is tosay a surface temperature within a given defined temperature range,during the production of all the layers, it is ensured that theoccurrence of surface stresses which arise when cooling of thethree-dimensional body is too great is reduced. This in turn leads tothe end product having a reduced occurrence of shape deviations and alsoa reduced occurrence of internal stresses in the end product.

DESCRIPTION OF FIGURES

The invention will be described in greater detail below in connectionwith accompanying drawing figures, in which:

FIG. 1 shows a cross section of an arrangement according to theinvention,

FIG. 2 shows an area to be fused together, which has an inner area andan edge,

FIG. 3 shows a further division of the area to be fused together into aset of separate areas having respective inner areas and edges,

FIG. 4 shows diagrammatically an example of how a number of adjacentinner areas are treated in a first process step, after which edgesbelonging to said adjacent part areas are fused together in a second,subsequent process step,

FIG. 5 shows a selected area which is divided into a very great numberof inner areas in a squared pattern,

FIG. 6 shows a number of consecutive powder layers where the edges arefused together with intermediate new powder application, after which theinner areas of several powder layers are treated in a common subsequentprocess step,

FIG. 7 shows FIG. 6 seen from above,

FIG. 8 shows a set of different curve shapes with a one-dimensionalinterference term,

FIG. 9 shows diagrammatically how the heat distribution appears in abody where the focal point with the diameter D of a radiation gun hasheated the body, on the one hand in the presence of an interference termon the other hand in the absence of an interference term,

FIG. 10 shows an example of the movement of the focal point in relationto movement of the focal point along the main movement direction,

FIG. 11 shows a set of different curve shapes with a two-dimensionalinterference term,

FIG. 12 shows the movement pattern of a focal point according to apreferred embodiment of the invention,

FIG. 13 shows the positioning of the focal points and also a widenedarea within which fusing together takes place,

FIG. 14 shows diagrammatically a cross section of a three-dimensionalbody formed by a number of powder layers and also a top powder layer,

FIG. 15 shows a selected area which is divided into a set of separateareas,

FIG. 16 shows a schematic model for calculating energy balance,

FIG. 17 shows another schematic model for calculating energy balance,

FIG. 18 shows a view from the side of a chamber provided with atransparent window,

FIG. 19 shows an arrangement for feeding and fixing a protective filmfor maintaining the transparency of the window,

FIG. 20 shows diagrammatically a method for production ofthree-dimensional bodies,

FIG. 21 shows a flow diagram for generating primary operating schemes,

FIG. 22 shows a flow diagram for an operating scheme of the arrangement,

FIG. 23 shows a flow diagram for correction of said operating scheme,

FIG. 24 shows diagrammatically a procedure comprising correction ofoperating schemes with the aid of information obtained from a camerawhich measures the temperature distribution over the surface of thepowder bed,

FIG. 25 shows diagrammatically a procedure for correction of operatingschemes,

FIG. 26 shows a diagrammatic construction of a three-dimensionalarticle, and

FIG. 27 shows a number of cross sections from FIG. 26, and

FIG. 28 shows an embodiment of a function used for a heat transfercoefficient.

MODE(S) FOR CARRYING OUT THE INVENTION

FIG. 1 shows an arrangement for producing a three-dimensional productgenerally designated by 1. The arrangement comprises a work table 2 onwhich a three-dimensional product 3 is to be built up, one or morepowder dispensers 4 and also means 28 which are arranged so as todistribute a thin a layer of powder on the work table 2 for forming apowder bed 5, a radiation gun 6 for delivering energy to the powder bed,fusing together of parts of the powder bed then taking place, means 7for guiding the beam emitted by the radiation gun 6 over said work tablefor forming a cross section of said three-dimensional product by fusingtogether said powder, and a control computer 8 in which informationabout successive cross sections of the three-dimensional product isstored, which cross sections build up the three-dimensional product. Ina work cycle, the work table will, according to the preferred embodimentshown, be lowered gradually in relation to the radiation gun after eachpowder layer applied. In order to make this movement possible, the worktable is, in a preferred embodiment of the invention, arranged movablyin the vertical direction, that is to say in the direction indicated bythe arrow P. This means that the work table starts in a startingposition 2′ in which a first powder layer of the necessary thickness hasbeen applied. So as not to damage the underlying work table and in orderto provide this layer with sufficient quality, this layer is thickerthan other layers applied, fusing through of this first layer then beingavoided. The work table is subsequently lowered in connection with a newpowder layer being distributed for forming a new cross section of thethree-dimensional product. In one embodiment of the invention, the worktable is to this end supported by a stand 9 which comprises at least oneball screw 10, provided with toothing 11. A step motor or servomotor 12provided with a gearwheel 13 sets the work table 2 to the desiredvertical position. Other arrangements known to the expert for settingthe working height of a work table can also be used. Adjusting screws,for example, can be used instead of racks. According to an alternativeembodiment of the invention, means for powder distribution included inthe arrangement can be raised gradually instead of lowering the worktable as in the embodiment described above.

The means 28 is arranged so as to interact with said powder dispensersfor replenishment of material. Furthermore, the sweep of the means 28over the working surface is driven in a known manner by a servomotor(not shown) which, moves the means 28 along a guide rail 29 which runsalong the powder bed.

When a new powder layer is applied, the thickness of the powder layerwill be determined by how much the work table has been lowered inrelation to the previous layer. This means that the layer thickness canbe varied according to requirements. It is therefore possible, when across section has a great change in shape between adjacent layers, tomake thinner layers, a higher surface fineness then being achieved, and,when there is little or no change in shape, to make layers with maximumpenetration thickness for the beam.

In a preferred embodiment of the invention, the radiation gun 6 consistsof an electron gun, the means 7 for guiding the beam of the radiationgun consisting of deflecting coils 7″. The deflecting coil generates amagnetic field which guides the beam produced by the electron gun, itthen being possible for fusion of the surface layer of the powder bed inthe desired location to be brought about. The radiation gun alsocomprises a high-voltage circuit 20 which is intended to provide theradiation gun in a known manner with an acceleration voltage for anemitter electrode 21 arranged in the radiation gun. The emitterelectrode is in a known manner connected to a current source 22 which isused to heat the emitter electrode 21, electrons then being released.The functioning and composition of the radiation gun are well-known toan expert in the field.

The deflecting coil is controlled by the control computer 8 according toan operating scheme laid out for each layer to be fused together, itthen being possible to guide the beam according to a desired operatingscheme. Details of the appearance according to the invention of theoperating scheme are described below in connection with the descriptionof FIGS. 2-9.

Also present is at least one focusing coil 7′ which is arranged so as tofocus the beam on the surface of the powder bed on the work table.Deflecting coils 7″ and focusing coils 7′ can be arranged according to anumber of alternatives well known to the expert.

The arrangement is enclosed in a casing 15 which encloses the radiationgun 6 and the powder bed 2. The casing 15 comprises a first chamber 23which surrounds the powder bed and a second chamber 24 which surroundsthe radiation gun 6. The first chamber 23 and the second chamber 24communicate with one another via a passage 25 which allows emittedelectrons, which have been accelerated in the high-voltage field in thesecond chamber, to continue into the first chamber, subsequently tostrike the powder bed on the work table 2.

In a preferred embodiment, the first chamber is connected to a vacuumpump 26 which lowers the pressure in the first chamber 23 to a pressureof preferably roughly 10⁻³-10⁻⁵ mbar. The second chamber 24 ispreferably connected to a vacuum pump 27 which lowers the pressure inthe second chamber 24 to a pressure of roughly 10⁻⁴-10⁻⁶ mbar. In analternative embodiment, both the first and second chambers can beconnected to the same vacuum pump.

The control computer 8 is furthermore preferably connected to theradiation gun 6 for regulating the output of the radiation gun and alsoconnected to the step motor 12 for adjusting the vertical position ofthe work table 2 between consecutive applications of powder layers, itthen being possible to vary the individual thickness of the powderlayers.

The control computer is also connected to said means 28 for powderdistribution on the working surface. This means is arranged so as tosweep over the working surface, a layer of powder being distributed. Themeans 28 is driven by a servomotor (not shown) which is controlled bysaid control computer 8. The control computer controls the sweep alongand ensures that powder is replenished as required. For this reason,load sensors can be arranged in the means 28, the control computer thenbeing able to obtain information about the means being empty or havingbecome stuck.

According to a preferred embodiment of the invention, the controlcomputer 8 is also arranged so as to calculate an energy balance for theselected area to be treated within each powder layer, it beingdetermined in the calculation whether energy radiated into the selectedarea from the surroundings of the selected area is sufficient tomaintain a defined working temperature of the selected area.

FIG. 2 shows diagrammatically an area 35 to be fused together. The areacomprises an inner area I delimited by an edge R. According to theinvention, the operating scheme is designed in such a way that the areato be fused together, that is to say the selected area, is divided intoone or more inner areas 1, each having an edge R. An inner area ispreferably treated in a process step which is separate from thetreatment of the edge which surrounds the inner area. Separate processstep means that the edge is finished either before or after the innerarea.

FIG. 3 shows diagrammatically an area 35 to be fused together. This areais divided into a number of part areas 80-91 which each have an innerarea and an edge. According to a first preferred embodiment of theinvention, the inner area I of a set of adjacent part areas is fusedtogether in a first process step, after which said edges R are fusedtogether and connect said part areas in a second, subsequent processstep. By means of this procedure, the occurrence of bending stresses inthe three-dimensional body after cooling is reduced.

FIG. 4 shows diagrammatically an example of how a number of adjacentinner areas are treated in a first process step comprising fusingtogether of the inner area 86, which has been carried out using a firstoperating scheme 1′. The operating scheme 1′ shown comprises a partlyoverlapping helical movement in accordance with the description below.The inner area 81 is then fused together according to a second operatingscheme 2′. The inner area 80 is also fused together according to a thirdoperating scheme 3′. Finally, the inner area 88 is fused togetheraccording to a fourth operating scheme 4′. In this way, a set ofadjacent part areas has been fused together in a first process step.Subsequently, the edges which surround the adjacent part areas 80, 81,86, 88 are fused together. This is effected according to a fifthoperating scheme 5′ which comprises fusing together the outer edge and asixth operating scheme 6′ comprising the inner edges which delimit thepart areas from one another.

According to a second preferred embodiment, the operating scheme isarranged so as to determine the priority for treating said plurality ofsmaller part areas with the aid of a random number generator. To thisend, the control computer 8 comprises a random number generator S. Thismethod is especially advantageous if the selected area is divided into avery great number of smaller part areas, preferably more than 100 or1000. An example of such division is shown in FIG. 5 where a selectedarea 35 is divided into a very great number of inner areas in a squaredpattern. A random priority shows how a series of areas 1″-6″ is treatedconsecutively.

According to a preferred embodiment, the random process can also includeintelligent selection where areas which are adjacent to an area whichhas just been heated are given less probability of being picked as thenext area. A heat camera used in the method can be arranged so as tomeasure the temperature of all the areas included and then adjustprobabilities depending on the temperature of each smaller area. If Nareas are used and the bed temperature varies from T₀, which correspondsto the uninfluenced bed temperature, to T_(S), which corresponds to thetemperature of an area which has just been fused, the probability of anarea being selected is preferably adjusted to P(i)=T_(S)−Ti/Σ(T_(S)−Tn).An area which has just been fused will then be given the probability 0of being heated again. The probability for all cold areas is equal, andthe probability of an area being selected to be the next area fortreatment is linearly dependent on the temperature in relation to thefusion temperature. Instead of using a heat camera, the probability canbe logically controlled and, for selection of a point, increase with thedistance from a point which has just been selected. The probabilitycalculation is preferably prepared on the basis of information from thethermal conductivity equation. When a very great number of part areas isfused together, the calculation for adjusting probabilities becomescomplicated. For this reason, it is advantageous to make use of the heatcamera described above.

In an alternative embodiment, the edges can be fused together in a firstprocess step and the inner areas in a subsequent process step. This canbe advantageous when very thin powder layers are distributed, a solidlateral surface being created, if appropriate with a number of innersupporting partitions. The inner areas can then be fused together in asubsequent process step where several powder layers are fused togetherin a common sweep of the radiation gun over several layers. This resultsin the inner areas being lightly sintered, which can be advantageous forcertain products. According to this third embodiment of the invention,edges are fused together in a first process step for a number ofconsecutive powder layers, after which the inner areas of saidconsecutive powder layers are fused together in a common, second processstep for said consecutive powder layers. This is shown diagrammaticallyin FIGS. 6 and 7.

FIG. 6 shows a number of consecutive layers i, i-1, i-2 where the edges1′″, 2′″, 3′″ have been fused together with intermediate new powderapplication. After this, the inner areas I (FIG. 7) have been fusedtogether in a process step common to several layers i, i-1, i-2. As athicker layer is applied, this method is suitable especially for forminga body with a smooth outer surface and internal partitions correspondingto the inner edges where the internal partitions have a high degree ofsolidity. The intermediate inner areas have a lower degree of fusingtogether, it being possible for a certain porosity to be obtained. Asthe product in this case is advantageously not entirely homogeneous, therisk of the appearance of internal stresses is reduced as a certaincapacity for movement in the inner porous structure allows internalstresses to be attenuated.

According to a preferred embodiment of the invention, the inner area Iis fused together using a movement pattern for the focal point of thebeam of the radiation gun which comprises a main movement direction andan interference term which is added to said main movement direction andhas a component in a direction at right angles to the main movementdirection. The interference term changes direction and has a time meanvalue corresponding to zero drift from the main movement direction. FIG.8 shows three different examples of different appearances of theinterference term which give rise to a movement in the form of atriangular wave, a sinusoidal curve and a square wave. At least thatedge which forms an inner or outer lateral surface of the finished bodyis preferably fused together in the course of a movement which followsthe edge without addition of an interference term.

FIG. 9 shows diagrammatically how the heat distribution appears in abody where the focal point with the diameter D of a radiation gun hasheated the body. The temperature distribution around the focal point hasthe shape of a Gaussian bell. The temperature distribution around afocal point without interference term is shown by the curve marked (α).By means of the interference term, the trace treated in the course ofpropagation of the beam along the main movement direction is widened. Awidened trace is shown by the curve indicated by (β). The widened tracealso has a temperature distribution with a lower maximum value. Thisreduces the risk of the appearance of overheating with the formation ofirregularities as a consequence.

The interference term is preferably of such a nature that a fusion zoneis formed which has a width essentially corresponding to twice theamplitude of the component of the interference term in a direction atright angles to the main movement direction. The average speed of theabsolute value of the movement of the focal point in the direction ofthe interference term is preferably to exceed the speed of the heatpropagation in the material. The speed in the main movement directionpreferably corresponds to the speed of the heat propagation in thematerial. The amplitude and the frequency of the interference term arepreferably to be adapted in such a way that the focal point is able tomove from its starting position where the interference term has thevalue zero, pass through the minimum and the maximum value of theinterference term and return to its position in the time it takes thewave front of the heat propagation to move from the first zero positionto the second zero position. This is shown diagrammatically in FIG. 10.FIG. 10 shows how the focal point moves along the curve 50 from a firstposition 51, past a maximum 52 of the interference term, a minimum 53 ofthe interference term and then takes up a second position 54 with a zerovalue of the interference term. During this time, the wave front of theheat propagation has been propagated from the first position 51 to thesecond position. If the average speed of the interference term is toolow, a curved fused trace which runs within the path defined by the endpoints of the interference term is formed instead of a wide trace.

According to a preferred embodiment, the interference term also has acomponent in a direction parallel to the main movement direction. Theinterference term is in this case two-dimensional. Examples ofinterference terms with a two-dimensional direction are given in FIG.11.

The edge R is preferably fused together in the course of a mainlyrectilinear movement of the beam of the radiation gun.

The purpose of operating with a movement pattern for the focal point ofthe beam of the radiation gun which comprises a main movement directionand an interference term added to said main movement direction which hasa component in a direction at right angles to the main movementdirection is that, with a wider trace, it is possible to move the fusionzone more slowly but still fuse at a relatively high speed compared withconventional operation.

Slow movement of the fusion zone produces less vaporization and areduced incidence of fused material boiling and splashing. The purposeof the edge being fused together using a continuous mainly rectilinearmovement is that this produces a smooth surface structure for thefinished product.

An analysis of the movement pattern for the beam of the radiation gun inthe case of a preferred embodiment of the invention with atwo-dimensional interference term, which gives rise to a helix-likemovement pattern of the focal point, follows below.

The position of a focal point which rotates about the x axis and movesalong the same axis at the speed V_(x) can be obtained from:r (t)=(V _(x) t+A _(x) cos(ωt)) x+A _(y) sin(ωt) y   Equ. 1where A_(x) and A_(y) are the amplitudes in the x and y directionrespectively. A typical “spinning curve” can appear like that shown inFIG. 12.

The pattern shown in FIG. 12 is obtained if ω is set to:

$\begin{matrix}{\omega = \frac{2\pi\; V_{x}}{A_{x}}} & {{Equ}.\mspace{14mu} 2}\end{matrix}$

The speed of the focal point is given by:

$\begin{matrix}{\frac{\mathbb{d}\overset{\_}{r(t)}}{\mathbb{d}t} = {{\left( {V_{x} - {A_{x}\omega\;{\sin\left( {\omega\; t} \right)}}} \right)\overset{\_}{x}} + {A_{y}\omega\;{\cos\left( {\omega\; t} \right)}\overset{\_}{y}}}} & {{Equ}.\mspace{14mu} 3}\end{matrix}$

Its absolute speed is therefore:

$\begin{matrix}{{\frac{\mathbb{d}\overset{\_}{r(t)}}{\mathbb{d}t}} = \sqrt{\left( {V_{x} - {A_{x}\omega\;{\sin\left( {\omega\; t} \right)}}} \right)^{2} + \left( {A_{y}\omega\;{\cos\left( {\omega\; t} \right)}} \right)^{2}}} & {{Equ}.\mspace{14mu} 4}\end{matrix}$

If the focal point moves according to the formulas above, its speed willvary and either be at a maximum underneath the x axis and a minimumabove or vice versa depending on the direction of rotation. In order toobtain a focal point which moves at constant speed along the spinningcurve in FIG. 12, its average speed is first calculated:

$\begin{matrix}{{V_{average} = \frac{\int_{0}^{T}{{\frac{\mathbb{d}\overset{\_}{r(t)}}{\mathbb{d}t}}\ {\mathbb{d}t}}}{T}}{{Where}\text{:}}{T = \frac{2\pi}{\omega}}} & {{Equ}.\mspace{14mu} 5}\end{matrix}$

V_(average) is the speed at which the focal point is to move. At thetime t, the focal point has moved the distance:s=t*V _(average)

This distance must be equal to the spinning curve length at the time t′.Therefore:

$\begin{matrix}{s = {{t*V_{average}} = {\int_{0}^{t^{\prime}}{{\frac{\mathbb{d}\overset{\_}{r(t)}}{\mathbb{d}t}}\ {\mathbb{d}t}}}}} & {{Equ}.\mspace{14mu} 6}\end{matrix}$

Solving Equ. 6 for 0<t<T gives t′ as a function of t. t′ is then used inEqu. 1 which gives the position of the spot as a function of the time t.

A number of simulations using different speeds and Ay has shown that thefusion zone 0.1-0.15 mm below the surface has an approximate width of1.8Ay. The hop between two spin lines should then be:Hop spin=1.8Ay−0.3

The distance to the start from an edge is approximately:Starting hop=0.8Ay−0.15

FIG. 13 shows a continuous wide fused edge which propagates in thedirection x marked by an arrow in the diagram. The focal points with adiameter D are marked in the diagram. The overlapping pattern ensuresthat fusing together takes place within an area outside the focal point.Such an area is illustrated and marked by the symbol δ. Together, theseareas form an overall area which propagates in the direction marked bythe arrow x.

According to a preferred embodiment of the invention, the controlcomputer is also arranged so as to calculate an energy balance for atleast the selected area to be fused together within each powder layer,it being determined in the calculation whether energy radiated into theselected area from the surroundings of the selected area is sufficientto maintain a defined working temperature of the selected area.

The purpose of calculating the energy balance for the powder layers isto calculate the power required in order to keep the surface of theobject at a given temperature. The power is assumed to be constant overthe entire surface.

How the energy balance calculation is performed in an embodiment of theinvention where the calculation is performed for one layer at a time isdescribed below.

In order for it to be possible to calculate the power in real time,simplifications are necessary:

-   1. We imagine that the temperature is constant in the x and y    directions and that it varies only in the z direction, in other    words the entire surface has the same temperature.-   2. The temperature in the z direction varies with jLt, where j is    the layer number and Lt is the layer thickness.-   3. The temperature distribution during fusion is assumed to be    stationary.

The following parameters have an effect on the calculation:

Various indexes:

-   i=index for the top layer-   j=layer index goes from 1 to i    Object data:-   Lt=layer thickness to be fused [m]-   Lcont(j)=contour length for layer j [m]-   Apowt(z)=Apow(j)=area facing the powder for layer j [m]-   A(z)=A(j) total surface area fused for layer j [m²]    Material properties:-   λ_(met)=thermal conductivity of the material [W/mK]-   σ_(met)=radiation constant for the metal surface [W/m²K]-   σ_(metpow)=radiation constant for metal surface covered with powder    [W/m²K]-   σ_(pow)=radiation constant for the powder surface [W/m²K]-   λ_(pow)=thermal conductivity of the powder [W/mK]-   h_(pow)(z)=heat transfer coefficient from the object out to the    powder [W/m²K]-   α=proportion of the radiation power taken up by the material    Temperatures [K]:-   Tsur(i)=temperature of the surroundings affecting the surface when    layer i is fused (can be measured on the heating shield)-   Tpow(z)=temperature in the powder-   T(z)=temperature in the object-   Tsurf(i)=T(iLt)=desired temperature on the surface of the object    when layer i is fused. (Is set in AMA)-   Tbott(i)=temperature at the bottom of the object before layer i is    started (Is measured just before raking or is calculated. See    below.)

In order to determine how the temperature is distributed in the object,we solve the one-dimensional stationary thermal conductivity equationincluding a source term which takes account of heat losses out into thepowder:

${{- \lambda_{met}}\frac{\partial^{2}{T(z)}}{\partial z^{2}}} = {\frac{{h_{pow}(z)}{{Apow}(z)}}{{A(z)}{Lt}}\left( {{{Tpow}(z)} - {T(z)}} \right)}$

The boundary conditions on the surface and at the bottom are:

$\left. {{- \lambda_{met}}\frac{\partial{T(z)}}{\partial z}} \right|_{z = {iLt}} = {\left. {{\frac{\left( {\sigma_{met} + \sigma_{pow}} \right)}{2}\left( {{T({iLt})}^{4} - {{Tsur}(i)}^{4}} \right)} - \frac{P_{in}}{A({iLt})} - {\lambda_{met}\frac{\partial{T(z)}}{\partial z}}} \right|_{z = 0} = {h_{pow}\left( {{{Tbott}(i)} - {T(0)}} \right)}}$Where A and B are two constants.

Rewrite the formulas as differential formulas instead and let j beindexed for each layer.

${{- \lambda_{met}}\frac{{T\left( {j + 2} \right)} - {2{T\left( {j + 1} \right)}} + {T(j)}}{{Lt}^{2}}} = {{{\frac{{h_{pow}(j)}{{Apow}(j)}}{{A(j)}{Lt}}\left( {{{Tpow}(j)} - {T(j)}} \right)} - {\frac{\lambda_{met}}{Lt}\left( {{T(i)} - {T\left( {i - 1} \right)}} \right)}} = {{{\frac{\left( {\sigma_{met} + \sigma_{pow}} \right)}{2}\left( {{T(i)}^{4} - {{Tsur}(i)}^{4}} \right)} - \frac{P_{in}}{A(i)} - {\frac{\lambda_{met}}{Lt}\left( {{T(2)} - {T(1)}} \right)}} = {h_{pow}\left( {{{Tbott}(i)} - {T(1)}} \right)}}}$where 1 ≤ j ≤ i − 2

The boundary condition on the surface actually provides us with nothingnew as far as the temperature distribution in the object is concerned asthe temperature of the surface is determined by T(i). But it is requiredin order to determine Pin which is the power necessary in order to keepthe temperature on the surface at T(i). T(j) is now obtained from thefollowing equation system:

${\Delta(j)} = {- \frac{{h_{pow}(j)}{{Apow}(j)}{Lt}}{{A(j)}\lambda_{met}}}$T(j + 2) − 2T(j + 1) + T(j)(1 + Δ(j)) = Δ(j)Tpow(j)${T(1)} = {{{{Tbott}(i)}\frac{{h_{pow}(1)}{{Lt}/\lambda_{met}}}{\left( {1 + {{h_{pow}(1)}{{Lt}/\lambda_{met}}}} \right)}} + {{T(2)}\frac{1}{\left( {1 + {{h_{pow}(1)}{{Lt}/\lambda_{met}}}} \right)}}}$

Insert the expression pressure for T(1) and formulate the problem as alinear equation system:

${{1.\mspace{14mu}{T(3)}} - {2{T(2)}} + {{T(2)}\frac{\left( {1 + {\Delta(1)}} \right)}{\left( {1 + {{h_{pow}(1)}{{Lt}/\lambda_{met}}}} \right)}}} = {{{\Delta(1)}{{Tpow}(1)}} - {{{Tbott}(i)}\frac{{h_{pow}(1)}{{Lt}/\lambda_{met}}}{\left( {1 + {{h_{pow}(1)}{{Lt}/\lambda_{met}}}} \right)}\left( {{1 + {{\Delta(1)}2.\mspace{14mu}{T(4)}} - {2{T(3)}} + {{T(2)}\left( {1 + {\Delta(2)}} \right)}} = {{{{\Delta(2)}{{Tpow}(2)}1\text{-}2.}\mspace{14mu} - {2{T\left( {i - 1} \right)}} + {{T\left( {i - 2} \right)}\left( {1 + {\Delta\left( {i - 2} \right)}} \right)}} = {{{\Delta\left( {i - 2} \right)}{{Tpow}\left( {i - 2} \right)}} - {T(i)}}}} \right.}}$In matrix form this becomes:

Ax = b where  then: $\begin{matrix}{A_{jk} = {{\delta\mspace{11mu}\left( {j + 1 - k} \right)} - {2\delta\mspace{11mu}\left( {j - k} \right)} + {\delta\mspace{11mu}\left( {j - 1 - k} \right)\left( {1 + {\Delta\mspace{11mu}(j)}} \right)} +}} \\{\delta\mspace{11mu}\left( {1 - k} \right)\mspace{11mu}\delta\mspace{11mu}\left( {1 - j} \right)\frac{\left( {1 + {\Delta\mspace{11mu}(1)}} \right)}{\left( {1 + {{h_{pow}(1)}\mspace{11mu}{{Lt}/\lambda_{met}}}} \right)}}\end{matrix}$ x_(l) = T  (2), …  , x_(l − 2) = T  (i − 1)$\begin{matrix}{b_{j} = {{\Delta\mspace{11mu}(j)\mspace{11mu}{Tpow}\mspace{11mu}(j)} - {\delta\mspace{11mu}\left( {j - 1} \right)\mspace{11mu}{Tbott}\mspace{11mu}(i)\frac{{h_{pow}(1)}\mspace{11mu}{{Lt}/\lambda_{met}}}{\left( {1 + {{h_{pow}(1)}\mspace{11mu}{{Lt}/\lambda_{met}}}} \right)}}}} \\{\left( {1 + {\Delta\mspace{11mu}(1)}} \right) - {\delta\mspace{11mu}\left( {j - i + 2} \right)\mspace{11mu} T\mspace{11mu}(i)}}\end{matrix}$

In order for it to be possible to solve the equations, it is necessarythat the temperature of the powder, Tpow(j), and the heat transfercoefficient, h_(pow)(j), are known. In the program, Tpow(z) is set to:Tpow(j)=AT(j)_(i−1) +BTsur(i−1)i−1 means that the temperature for the previous layer is used in orderto determine Tpow(j).

The function used for h_(pow)(j) is depicted in FIG. 28.

The values L1 and L2 have been assumed to be area-independent whilehconst1, hconst2 and hconst3 are assumed to depend on A(j). All theconstants in the expressions for both Tpow and hpow have been producedby adapting the 1D model above to 3D FEM calculations on objects withsimple geometries.

Included in the expression for the source term is Apow(j) which isactually the total area facing the powder for each layer. In the case oflarge area transitions, this value may be very great, which means thatthe value of the source term jumps. Such discrete jumps make thesolution unstable. In order to prevent this, according to a preferredembodiment, Apow(j) is set to Lcont(j)*Lt. Power losses which ariseowing to an area transition are instead added afterwards. The size ofthe power loss depends on how large over the respective underlying areathe area transition is and how far below the top layer it is located.The values for different area transitions and different depths have beenproduced by 3D FEM simulations. For an arbitrary area transition, theadditional power is obtained by interpolation.

Before the power is calculated, the program reads the various values forLcont(j)*Lt and A(j) for each layer. With the aid of a script file,these can be influenced in various ways. In this way, it is possible tocontrol the power for each layer. How the various geometry parametersare influenced emerges from the description of how the script filefunctions.

When the equation system above is solved, the total power required inorder to keep the surface at Tsuff(i) is obtained from the boundarycondition for the surface:

$P_{in} = {A\mspace{11mu}(i)\begin{pmatrix}{{\frac{\;\lambda_{\;{met}}}{\;{Lt}}\left( {{T\mspace{11mu}(i)} - {T\mspace{11mu}\left( {i - 1} \right)}} \right)} +} \\{\frac{\left( \mspace{11mu}{\sigma_{\;{met}}\mspace{11mu} + \mspace{14mu}\sigma_{\;{pow}}} \right)}{2}\left( {{T\mspace{11mu}(i)^{4}} - {{Tsur}\mspace{11mu}(i)^{4}}} \right)}\end{pmatrix}}$

When a layer is fused, use is made of different current and speed overthe surface. In order for it to be possible to calculate the differentcurrents required, the mean value of all powers used is set equal toPin.

If a layer is to be fused using n, different currents, then:

$P_{in} = {\alpha\; U\frac{\sum\limits_{k = 1}^{k = n_{1}}\;{I_{lk}t_{jk}}}{T_{tot}}}$$t_{ik} = \frac{l_{ik}}{v_{ik}}$$T_{tot} = {\sum\limits_{k = 1}^{k = n_{1}}\; t_{ik}}$Where t_(ik) is the fusion time for each current I_(ik)

-   I_(ik) is the fusion length-   v_(ik) is the fusion speed-   T_(tot) is the total fusion time for the layer i-   U is the acceleration voltage.

In order for it to be possible to calculate the currents, the speedsmust therefore be known. These are obtained from what are known as speedfunctions which indicate the relationship between current and speed. Asthese functions are not analytical, an iterative procedure must be usedin order to determine all the currents and speeds. In the calculationprogram, each starting value of I_(ik) is guessed. The various speedsare then obtained. The values of the currents are then increased untilthe mean value of the power just exceeds the calculated value of Pin.

Assume now that we want to fuse the various part areas at such a speedand current that the energy which is delivered to the material is lessthan that required in order to keep the surface at Tsurf(i). The surfacemust then be heated. The number of times required in order to heat thesurface is obtained by adding a heating term in the expression for themean value of the power:

$P_{i}^{heat} = \frac{n\;\alpha\;{Ul}_{i}^{heat}I_{i}^{heat}}{v_{i}^{heat}}$and adding the heating time in the expression for the time T_(tot):

$t_{i}^{heat} = \frac{n\; l_{i}^{heat}I_{i}^{heat}}{v_{i}^{heat}}$where n indicates how many times the surface has to be heated.

The calculation routine shown above can be used for the entire powderlayer. In an alternative embodiment, calculation can be carried out forvarious part areas of the powder layer. The equations indicated abovecan be used in this case as well. However, different boundary conditionsare obtained for the inner edges which lie close to a fused body.

FIG. 14 shows a side view of a fused-together body 30 which is built upby fusing together part areas 31-34 in consecutive powder layers i-1,i-2, i-3, i-4. A real body manufactured according to the invention canof course have many more layers than indicated in this example.

A top powder layer i is distributed on the body. Located within this toppowder layer is a selected area 35. The selected area 35 consists of thearea which, according to an operating scheme, is to be fused together.The selected area 35 within the layer i is delimited by an outer edge36. It is of course conceivable for a selected area to comprise bothouter and inner edges. The balance calculation is to be performed on theentire selected area 35. The selected area 35 is preferably divided intoa plurality of smaller part areas as shown in FIG. 15, it then beingpossible for separate calculations to be performed for the part areas.

FIG. 15 shows a selected area 35 which is divided into a plurality ofsmaller part areas 38-53, an energy balance being calculated for each ofsaid set of separate part areas 38-53. The selected area is delimited byan outer edge 72. The selected area can of course also comprise inneredges.

According to another preferred embodiment of the invention, said set ofseparate areas 38-53 comprises a first group of areas 54-58 of which theedges lie entirely within the selected area 35 and a second group ofareas 38-53 of which the edges coincide at least in part with the edge72 of the selected area. Where appropriate, the areas within said secondgroup of areas can be divided into sub-areas 38 a, 39 b; 48 a-48 d. Eachof the part areas 54-58 making up said first group of areas preferablyhas the same shape. In the example shown, the areas are square.Rectangular, triangular and hexagonal areas can advantageously be used.Boundary conditions within this group are also similar apart frompossible temperature differences. The use of likeness of shape allowsthe calculation routines to be simplified as in part common calculationscan be performed.

The energy balance is calculated in principle according toE^(in)(i)=E^(out)(i)+E^(heat)(i), where E^(in)(i) represents energy fedinto the part area, E^(out)(i) represents energy losses throughdissipation and radiation from the part area, and E^(heat)(i) representsstored in the part area. The energy fed in consists of on the one handenergy E^(in)(c) which has been radiated in or has flowed in via thermalconduction from the surroundings of the part area 35 for which theenergy balance is calculated and on the other hand of energy E^(in)(s)which has been radiated in from the radiation gun 6. If the energybalance is calculated befsore energy has been supplied to the part area35, E^(in)(s) therefore=0. According to a preferred embodiment of theinvention, at least a first energy balance calculation is performed forthe part area 35 before energy has been supplied via the radiation gun6.

FIG. 16 shows diagrammatically a model on which the calculation of theenergy balance for the part area Δ₁ is based. In this case, the partarea Δ₁ corresponds to a part of the selected area of the powder layeri. In this case, the equation for calculation of the energy balance hasthe appearance E^(in)(Δ₁)=E^(out)(Δ₁)+E^(heat)(Δ₁), where E^(in)(Δ₁)represents energy fed into the part area, E^(out)(Δ₁) represents energylosses through dissipation and radiation from the part area Δ₁ andE^(heat)(Δ₁) represents stored in the part area Δ₁. The energy fed inconsists of on the one hand energy E^(in(c))(Δ₁) which has been radiatedin or has flowed in via thermal conduction from the surroundings of thepart area Δ₁ and on the other hand of energy E^(in(s))Δ₁ which has beenradiated in from the radiation gun 6.

FIG. 17 shows diagrammatically a model on which the calculation of theenergy balance for a second part area Δ₂ within the selected area 35 inthe layer i is based. In this case, the part area Δ₂ corresponds to apart of the selected area 35 of the powder layer i which has not yetbeen fused together and which is adjacent to a first part area Δ₁ withinthe powder layer i, where radiation or thermal conduction takes placefrom said first to said second part area. In this case, the equation forcalculation of the energy balance has the appearanceE^(in)(Δ₂)=E^(out)(Δ₂)+E^(heat)(Δ₂), where E^(in)(Δ₂) represents energyfed into the part area, E^(out)(Δ₂) represents energy losses throughdissipation and radiation from the part area Δ₁ and E^(heat)(Δ₂)represents stored in the part area Δ₂. The energy fed in consists of onthe one hand energy E^(in(c))(Δ₂) which has been radiated in or hasflowed in via thermal conduction from the surroundings of the part areaΔ₁ and on the other hand of energy E^(in(s))Δ₂ which has been radiatedin from the radiation gun 6. The energy E^(in(c))(Δ₂) supplied viathermal conduction comprises the component E^(in(s))(Δ₂, i−1) whichcorresponds to energy supplied from the previous layer and also E^(out)(Δ₁, Δ₂) which corresponds to energy which has been dissipated orradiated from the first part area Δ₁ and supplied to the second partarea Δ₂.

According to FIG. 18, the arrangement also comprises, according to apreferred embodiment of the invention, means 14 for sensing surfaceproperties of a surface layer located in the powder bed. This means 14for sensing the temperature distribution of a surface layer located in apowder bed 5 preferably consists of a camera. In a preferred embodimentof the invention, the camera is used on the one hand to measure thetemperature distribution on the surface layer and on the other hand tomeasure the occurrence of surface irregularities by means of the shadowformation to which surface irregularities give rise. On the one hand,information about the temperature distribution is used to bring about asuniform a temperature distribution as possible over those parts of thesurface layer which are to be fused and, on the other hand, informationcan be used in order to check for any dimensional deviations betweengenerated three-dimensional product and original design as thetemperature distribution reflects the shape of the product. In apreferred embodiment of the invention, the video camera is mounted onthe outside of the casing 15 which encloses the powder bed 5 and theradiation gun 6. In order to make temperature measurement possible, thecasing is provided with a transparent window 16. The powder bed 5 isvisible for the camera through this window.

In a preferred embodiment of the invention, which is shown in FIG. 19,the window 16 is covered by a protective film 17. The protective film isfed from a feed-out unit 18 to a collecting unit 19, the film beinggradually replaced, which means that the transparency can be maintained.The protective film is necessary as coatings form as a consequence ofthe fusion process.

A detailed description relating to generating and correcting operatingschemes follows below in connection with the description of drawing FIG.20-.

FIG. 20 shows diagrammatically a method of producing three-dimensionalbodies according to the invention. The three-dimensional body is formedby successive fusing together of selected areas of a powder bed, whichparts correspond to successive cross sections of the three-dimensionalbody.

In a first method step 100, application of a powder layer to a worktable takes place. Application is effected by the means 28 mentionedabove distributing a thin layer of powder on the work table 2.

In a second method step 110, energy is supplied from a radiation gun 6,according to an operating scheme determined for the powder layer, to aselected area within the powder layer, fusing together of the area ofthe powder layer selected according to said operating scheme then takingplace to form a cross section of said three-dimensional body. Athree-dimensional body is formed by successive fusing together ofsuccessively formed cross sections from successively applied powderlayers. The successive cross sections are divided into one or more innerareas I, each having an edge R.

According to a first embodiment of the invention, the operating schemeis designed in such a way that the radiation gun fuses together theinner area I of a set of adjacent part areas in a first process step,after which said edges R are fused together and connect said part areasin a second, subsequent process step.

According to an alternative embodiment of the invention, the edges arefused together in a first process step for a number of consecutivepowder layers, after which the inner areas of said consecutive powderlayers are fused together in a common second process step for saidconsecutive powder layers.

According to a second embodiment of the invention, the operating schemeis arranged so as to determine the priority for treating said pluralityof smaller part areas with the aid of a random number generator.

In a preferred embodiment of the invention, the inner area is fusedtogether in the course of a movement pattern for the focal point of thebeam of the radiation gun which comprises a main movement direction andan interference term which is added to said main movement direction andhas a component in a direction at right angles to the main movementdirection. According to a preferred embodiment, the edge is fusedtogether in the course of a mainly rectilinear movement of the beam ofthe radiation gun.

In a preferred embodiment, an energy balance is calculated in a thirdmethod step 120 for at least the selected area to be fused togetherwithin each powder layer, it being determined in the calculation whetherenergy radiated into the selected area from the surroundings of theselected area is sufficient to maintain a defined working temperature ofthe selected area. Calculation is performed according to the modelsindicated above.

FIG. 21 shows diagrammatically the procedure for generating primaryoperating schemes. In a first step 40, a 3D model is generated, in a CADprogram for example, of the product to be manufactured, or alternativelya ready-generated 3D model of the product to be manufactured is inputinto the control computer 8. Then, in a second step 41, a matrixcontaining information about the appearance of cross sections of theproduct is generated. FIG. 25 shows a model of a hammer with examples ofassociated cross sections 31-33. These cross sections are also shown inFIG. 26 a-26 c. The cross sections are distributed with a densitycorresponding to the thickness of the various layers to be fusedtogether in order to form the finished product. The thickness canadvantageously be varied between the various layers. It is inter aliaadvantageous to make the layers thinner in areas where there is greatvariation in the appearance of the cross sections between adjacentlayers. When the cross sections are generated, a matrix containinginformation about the appearance of all the cross sections whichtogether make up the three-dimensional product is therefore created.

Once the cross sections have been generated, a primary operating schemeis generated for each cross section in a third step 42. Generation ofprimary operating schemes is based on shape recognition of the partswhich make up a cross section on the one hand and knowledge of how theoperating scheme affects the cooling temperature of local parts of across section on the other hand. The aim is to create an operatingscheme which allows the cooling temperature to be as uniform as possiblein the parts which are fused together before the next layer is appliedat the same time as the cooling temperature is to be kept within adesired range in order to reduce the risk of shrinkage stressesappearing in the product and to reduce the magnitude of shrinkagestresses which have arisen in the product, with deformation of theproduct as a consequence.

In the first place, a primary operating scheme is generated on the basisof the shape of separate component parts of the cross section. Whengeneration takes place, the edge and the inner area of each crosssection are identified. Where appropriate, a set of inner areas whicheach have edges is formed. According to the invention, an operatingscheme is generated for the inner areas which has a movement pattern forthe focal point of the radiation gun which comprises a main movementdirection and an interference term which is added to said main movementdirection and has a component in a direction at right angles to the mainmovement direction as indicated above. At the edges, the focal point ofthe radiation gun moves in a mainly linear movement pattern. This meansthat the radiation gun follows the shape of the edge.

In a preferred embodiment of the invention, primary operating schemesare therefore laid out on the basis of experience of which operatingschemes provide a good temperature distribution of the coolingtemperature of the cross section, it then being possible for the risk ofshrinkage stresses in the product with deformation of the product as aconsequence to be reduced. To this end, a set of operating schemes forareas of different shapes is stored in a memory. The operating schemesaccording to the invention are designed in such a way that the focalpoint of the radiation gun, within inner areas I, moves in a movementpattern which comprises a main movement direction and an interferenceterm which is added to said main movement direction and has a componentin a direction at right angles to the main movement direction. Inaddition to this information, the operating schemes can comprise a listof the order in which a set of inner areas is to be treated, informationabout heating different areas and information about energy supply andsweep speed. In a preferred embodiment, this memory is updated asresults of corrections of the operating scheme are evaluated, aself-learning system being obtained.

In an alternative embodiment of the invention, ready-finished crosssections, which have been generated by a stand-alone computer, are inputinto a memory in the control computer, where said primary operatingschemes are generated. In this case, information is provided directly tothe third step 42 via an external source 40 a.

FIG. 22 shows diagrammatically a procedure for generating athree-dimensional body, which comprises method steps for calculating anenergy balance for a layer. In a first method step 130, parameters onwhich an energy balance calculation is based are determined. In a secondmethod step 140, calculation of the energy balance for at least theselected area 35 takes place. Calculation is performed according to themethod illustrated previously.

In a third method step 150, the operating scheme is updated depending onthe calculated energy balance. If the result of the energy balance isthat sufficient heat energy is stored in the selected area to maintain adesired working temperature, no extra energy supply takes place.According to one embodiment of the invention, if the result of theenergy balance is that sufficient heat energy to maintain a desiredworking temperature is not stored in the selected area, an extra energysupply takes place in the form of preheating of the selected area beforefusing together takes place. This preheating can be effected by theradiation gun being swept very rapidly over the area or the radiationgun sweeping over the area with lower power than normal, oralternatively a combination of both of these. The preheating takes placein a fourth method step 160.

In a fifth method step 170, fusing together is effected by the radiationgun sweeping over the selected area.

FIG. 23 shows diagrammatically an embodiment of the invention which,where appropriate, utilizes the methods described above for generatingand correcting the operating schemes. In a first method step 180, one ormore of the inner areas I of the selected area are identified. In asecond method step 190, the edge or edges R which are associated withsaid inner areas and each surround said inner areas are identified. In athird method step 200, said inner areas I are fused together in thecourse of a partly overlapping circular movement of the beam emitted bythe radiation gun. During a fourth method step 210, said edges are fusedtogether in the course of a rectilinear movement of the beam. Themagnitude of the correction is smaller for processes which use themethod according to the invention with a movement pattern having aninterference term and also for processes where an energy balancecalculation is performed. A correction can nevertheless be used in orderfurther to improve the end result.

According to one embodiment of the invention, the operating scheme isarranged so as consecutively to fuse together the powder within one areaat a time within said inner areas.

According to a preferred embodiment of the invention, the controlcomputer is arranged so as to divide the surface within each powderlayer into a set of separate areas. The control computer is alsoarranged so as to ensure that said inner areas of a set of areas withinsaid first group of areas are fused together in the course of a partlyoverlapping circular movement of the beam of the radiation gun.

In one embodiment of the invention, the fusing together of the innerareas in said second group of areas takes place with a focal pointmovement comprising an interference term as described above. In analternative embodiment of the invention, the fusing together within theinner areas in said second group of areas takes place with a mainlyrectilinear movement.

According to a preferred embodiment of the invention, in the case of theembodiments described above relating to division of the selected surfaceinto smaller part surfaces, the calculation of energy balance describedabove is used in order to control the operating scheme with regard tocalibration of the power of the beam and supply of energy for heatingthe powder bed before final fusing together takes place.

FIG. 23 shows diagrammatically a procedure comprising correction ofoperating schemes with the aid of information obtained from a camerawhich measures the temperature distribution over the surface of thepowder bed. According to the procedure, the beam from the radiation gunis guided over the powder bed in order to generate a cross section of aproduct. In a first step 50, guidance of the beam over the powder bedaccording to the primary operating scheme defined in step 42 is started.In the next step 51, the temperature distribution on the surface layerof the powder bed is measured by the camera. From the measuredtemperature distribution, a temperature distribution matrix,T_(ij-measured), is then generated, in which the temperature of smallpart areas of the surface layer of the powder bed is stored. When thematrix is generated, each temperature value T_(ij-measured) in thematrix is compared with a desired value in a desired value matrixT_(ij-desired value). The surface layer of the powder bed can be roughlydivided into three categories. Firstly, areas where fusing togethertakes place by treatment by the radiation gun. In these areas, themaximum fusion temperature T_(ij-max) is of interest. Secondly, areaswhich have already been fused together and are thus cooling. In theseareas, a minimum permitted cooling temperature T_(ij-cooling-min) is ofinterest because too cold a cooling temperature gives rise to stressesand thus deformations of the surface layer. Thirdly, areas which havenot been treated by the radiation gun. In these areas, the bedtemperature T_(ij-bed) is of interest. It is also possible for thetemperature to be compared only in treated areas, T_(ij-bed) not thenbeing stored and/or checked.

In a third step 52, it is investigated whether T_(ij-measured) deviatesfrom the desired value T_(ij-desired value) and whether the deviation isgreater than permitted limit values. Limit values ΔT_(ij-max),ΔT_(ij-cooling) and ΔT_(ij-bed) associated with the three differentcategories are stored in the control computer 8. It is also possible forthe bed temperature not to be checked. In this case, the associatedlimit value is not stored. If the deviation between T_(ij-measured) andT_(ij-desired value) does not exceed this limit value, it isinvestigated in a fourth step 53 whether the surface layer is fullytreated. If this is not the case, operation according to the currentoperating scheme continues, method steps 50-53 mentioned above being runthrough once again.

If the deviation between T_(ij-measured) and T_(ij-desired value)exceeds one of said limit values, correction of the operating scheme 42takes place in a fifth step. In a preferred embodiment, said correctionis carried out according to the system shown in FIG. 24.

In a preferred embodiment of the invention, a new powder layer isdistributed only after completion of each layer, the product being builtup by successive fusing together of powder layers until the product isfinished. In this case, after a sixth step 55, a new layer is started,if the product as a whole is not finished, when it has been establishedin the fourth step 53 that the operating scheme for a layer has beencompleted.

In a preferred embodiment, the correction of the operating schemecomprises the following method steps:

in a first step 56, T_(ij-max) is compared withT_(ij-max-desired value). If T_(ij-max) deviates fromT_(ij-max-desired value) exceeding ΔT_(ij-max), the energy supply to thepowder layer is calibrated in a step 56 a by either changing the powerof the beam or changing the sweep speed of the beam.

In a second step 58, T_(ij-cooling) is compared withT_(ij-cooling-desired value). If T_(ij-cooling) deviates fromT_(ij-cooling-desired value) exceeding ΔT_(ij-cooling), the operatingscheme of the beam is changed in a step 58 a. There are many ways ofchanging the operating scheme of a beam. One way of changing theoperating scheme is to allow the beam to reheat areas before they havecooled too much. The radiation gun can then sweep over areas alreadyfused together with a lower energy intensity and/or at a higher sweepspeed.

In a third step 60, it is investigated whether T_(ij-bed) deviates fromT_(ij-bed-desired value). If the deviation is greater than ΔT_(ij-bed),the temperature of the bed can, in one embodiment of the invention, becorrected in a step 60 a, for example by the beam being made to sweepover the bed to supply energy. It is also possible to connect separatebed-heating equipment to the arrangement.

It is also possible for a size check of the article being manufacturedto be carried out by the heat camera installed in the arrangement. Asdescribed above, the bed and the parts which have been fused togetherare measured. The measured heat distribution reflects fully the shape ofthe object in a section of the three-dimensional body to be created. Acheck of the dimensions of the article can in this way be carried out ina fourth step 62, and feedback of X-Y deflection of the beam of theradiation gun is thus possible. In a preferred embodiment of theinvention, this check of the deviation between dimensions of the crosssection is carried out in a step 62 a and, if the deviation is greaterthan permitted, the X-Y deflection of the radiation gun is corrected.

Moreover, input signals from the camera can be used for identifying theoccurrence of surface irregularities, for example in the form of awelding spark. When the coordinates of a surface irregularity have beenidentified, the operating scheme can be updated so that the radiationgun is ordered to the identified coordinate in order to melt down thesurface irregularity.

The invention is not limited to the illustrative embodiment describedabove; the radiation gun can consist of, for example, a laser, in whichcase the deflection means consist of guidable mirrors and/or lenses.

The invention can furthermore be used in an arrangement for producing athree-dimensional product by energy transfer from an energy source to aproduct raw material, which arrangement comprises a work table on whichsaid three-dimensional product is to be built up, a dispenser which isarranged so as to distribute a thin layer of product raw material on thework table for forming a product bed, a means for delivering energy toselected areas of the surface of the product bed, a phase transition ofthe product raw material being allowed for forming a solid cross sectionwithin said area, and a control computer which manages a memory in whichinformation about successive cross sections of the three-dimensionalproduct is stored, which cross sections build up the three-dimensionalproduct, where the control computer is intended to control said meansfor delivering energy so that energy is supplied to said selected areas,said three-dimensional product being formed by successive joiningtogether of successively formed cross sections from product raw materialapplied successively by the dispenser.

In this case, the embodiment is not limited to fusing together powder bya radiation gun irradiating the surface of a powder bed. The product rawmaterial can consist of any material which forms a solid body after aphase transition, for example solidification after fusion or hardening.The energy-delivering means can consist of an electron gun or a laserguided over the working surface or alternatively of an energy-deliveringmeans which can project a cross section directly onto the product bed.

The embodiments described above can moreover be provided with all thefeatures described in relation to the embodiment described previously.

1. A method for production of three-dimensional bodies by successivefusing together of selected areas of a powder bed, which partscorrespond to successive cross sections of the three-dimensional body,the method comprising: applying powder layers to a work table,determining an operating scheme for the powder layer, supplying energyfrom a radiation gun, according to the operating scheme, to saidselected area within the powder layer, and fusing together that area ofthe powder layer selected according to said operating scheme for forminga cross section of said three-dimensional body, a three-dimensional bodybeing formed by successive fusing together of successively formed crosssections from successively applied powder layers, where fusing includesdividing said selected area into a plurality of smaller part areas whicheach comprise an inner area I and an edge R and said determining anoperating scheme includes determining priority for treating saidplurality of smaller part areas such that heating of the selected areatakes place in a relatively homogeneous way.
 2. The method as claimed inclaim 1, where fusing further includes fusing the inner areas I of a setof adjacent part areas in a first process step, and connecting theadjacent part areas by fusing the edges R belonging to said adjacentpart areas in a second process step, said second process step beingperformed after said first process step.
 3. The method as claimed inclaim 1 where said priority for treating is determined with the aid of arandom number generator.
 4. The method as claimed in claim 1, wherefusing further includes fusing said edges together in a first processstep for a number of consecutive powder layers, and fusing inner areasof said consecutive powder layers after fusing said edges in a commonsecond process step for said consecutive powder layers.
 5. The method asclaimed in claim 2 or 4, where fusing the inner areas includes fusingsaid inner areas together in the course of a movement pattern for thefocal point of the beam of the radiation gun, said movement patterncomprising a main movement direction and an interference term which isadded to said main movement direction and has a component in a directionat right angles to the main movement direction.
 6. The method as claimedin claims 2 or 4, where fusing said edges includes fusing said edgestogether in the course of a mainly rectilinear movement of the beam ofthe radiation gun.
 7. The method according to claim 1, the methodfurther including calculating an energy balance for at least one partarea within each powder layer, said calculating including determiningwhether energy radiated into the part area from surroundings of the partarea is sufficient to maintain a defined working temperature of the partarea.
 8. The method as claimed in claim 7, where said supplying energyincludes supplying, in addition to said energy for fusing together thepart area, energy for that heats the part area to a defined workingtemperature if the result of the energy balance calculation is thatsufficient energy for maintaining an intended working temperature of thepart area is not present.
 9. The method as claimed in claim 7 wherecalculating an energy balance includes calculating an energy balance foreach powder layer according to Ein(i) =Eout(i) +Eheat(i), where Ein(i)represents energy fed into the part area, Eout(i) represents energylosses through dissipation and radiation from the part area, andEheat(i) represents energy stored in the part area.
 10. The method asclaimed in claim 7, where calculating an energy balance includescalculating an energy balance for each of said part areas.
 11. Anarrangement for producing a three-dimensional product by successivefusing together of successively formed cross sections of said product,the arrangement comprising: a work table on which said three-dimensionalproduct is built up, a powder dispenser that forms a powder bed bydistributing a thin layer of powder on the work table, a radiation gundelivers energy to the powder, thereby fusing the powder together, beamguide that guides the beam emitted by the radiation gun over said powderbed such that radiation from said gun forms one of the cross sections ofsaid three-dimensional product by fusing together parts of said powderbed, and a control computer that stores information about the successivecross sections of the three-dimensional product, which cross sectionsbuild up the three-dimensional product, where the control computerdivides at least a selected area of each cross-section into a pluralityof smaller part areas which each comprise an inner area I and an edge R,and controls the radiation gun and beam guide according to an operatingscheme for forming each cross section of said three-dimensional productby determining a priority for delivering energy to said plurality ofsmaller part areas such that heating of the selected area takes place ina relatively homogeneous way.
 12. The arrangement as claimed in claim11, wherein the control computer controls the radiation gun and beamguide such that the radiation gun fuses together the inner area I of aset of adjacent part areas in a first process step, and connects saidpart areas by fusing together said edges R in a second, subsequentprocess step.
 13. The arrangement as claimed in claim 11 where thecontrol computer further includes a random number generator configuredsuch that the computer determines the priority for treating based onoutputs from said random number generator.
 14. The arrangement asclaimed in claim 11, where the control computer controls the radiationgun and beam guide such that the radiation gun fuses said edges togetherin a first process step for a number of consecutive powder layers, andthen fuses the inner areas of said consecutive powder layers together ina common second process step for said consecutive powder layers.
 15. Thearrangement as claimed in claims 12 or 14, where the control computercontrols the radiation gun and beam guide according to the operatingscheme such that the beam guide guides the focal point of the beam ofthe radiation gun within said inner areas using a movement pattern whichcomprises a main movement direction and an interference term which isadded to said main movement direction and has a component in a directionat right angles to the main movement direction.
 16. The arrangement asclaimed in claims 12 or 14, where the control computer controls theradiation gun and beam guide according to the operating scheme such thatthe radiation gun fuses together said edges in the course of a mainlyrectilinear movement of the beam of the radiation gun.
 17. Thearrangement as claimed in claim 11, where the control computercalculates an energy balance for at least one part area within eachpowder layer, and determines, based on the calculations, whether energyradiated into the part area from the surroundings of the part area issufficient to maintain a defined working temperature of the part area.18. The arrangement as claimed in claim 17, where the control computercontrols the delivery of energy to the powder according to the operatingscheme such that, in addition to energy for fusing together powderlayers, the radiation gun delivers energy for heating the powder layerif the result of the energy balance calculation is that the operatingscheme is not providing sufficient energy for maintaining an intendedworking temperature of the part area, a defined working temperature ofthe part area then being maintained.
 19. The arrangement as claimed inclaim 17, where the control computer calculates the energy balance foreach powder layer according to Ein(i)=Eout(i) +Eheat(i) where Ein(i)represents energy fed into the part area, Eout(i) represents energylosses through dissipation and radiation from the part area, andEheat(i) represents energy stored in the part area.
 20. The arrangementas claimed in claim 17, where the control computer calculates an energybalance for each of said part areas.
 21. The arrangement as claimed inclaim 11, the arrangement further comprising a temperature sensor thatsenses the temperature distribution of a surface layer located in thepowder bed.
 22. The arrangement of claim 11, where the radiation gunincludes at least one high-energy laser.
 23. The arrangement of claim11, where the radiation gun is an electron gun.